Here are two versions of tuna tartare, one of them a classic ceviche. Be sure not to marinate the tuna in the lime juice for too long or the meat will turn grey.
03In a medium bowl, combine the onion, garlic, chile, capers, avocado, salt, pepper and 2 tablespoons of the lime juice. Toss together gently. Add the tuna to the bowl.
04Stir together the remaining lime juice and the olive oil. Pour over the tuna, and toss the mixture together. Season to taste with salt and pepper. Cover and refrigerate for 15 minutes, stirring gently from time to time.
05Just before serving, add the cilantro and toss together. Taste and adjust seasonings. Line plates with salad greens, spoon the ceviche on top, and serve.